1. Field of the Invention
The present invention relates to an optical module used in optical communications or data communications.
2. Description of the Related Art
An optical module in which an optical element mounting substrate for mounting optical elements are arranged in a package has been used in optical communications or the like. Recently, in order to meet a requirement to save cost for the optical module, an optical module whose package is made of resin has heretofore been developed.
FIG. 7A is an exploded view of an optical module proposed in Japanese Patent Application No. Hei 9-007021 as an example of this type optical module. FIG. 7B is a perspective view of an example of an outer appearance of the optical module.
In the optical module 100 shown in FIGS. 7A and 7B, an array type optical element 1 in which, for example, light emitting portions or light receiving portions are arranged in an array is mounted on and fixed to an optical element mounting substrate 2. A pattern of electric signal wirings 10 is formed on a mounting surface (substrate surface) 28 of this optical element 1. Also, V-shaped grooves 9 (having a V-shape in cross section) as at least one pair of groove portions for positioning on the substrate side are formed on both sides with respect to the electric signal wirings 10.
There are various kinds of the optical elements 1. For example, there is a module in which a semiconductor laser chip having four channels for emitting an optical signal is arranged on a substrate, a module in which a photodiode chip for receiving an optical signal is arranged instead of the semiconductor laser chip, a module in which the semiconductor laser chip is arranged in the same manner and a photodiode chip for monitoring a light emission condition of the semiconductor laser chip is provided behind the semiconductor laser chip and the like. Among these optical elements, for example, the optical element that meets the specification is selected and mounted on and fixed to the optical element mounting substrate 2.
A package 4 is made of resin to have a base portion 31 and a side wall 32 having a substantially L-shape (an L-shape in cross section) that is in an upright position at an end face of the base portion 31. At least one (four in case of FIG. 7A) input/output optical fiber insertion hole 6 is formed in the side wall 32 of this package 4.
Input/output optical fibers 7 are inserted into the input/output optical fiber insertion holes 6, respectively. Each of the input/output optical fibers 7 is a short optical fiber for at least one of the optical input to the optical element 1 and the optical output of a beam outputted from the optical element 1 to the outside.
Further, a positioning projection 18 is formed in a position corresponding to each of the V-shaped grooves 9 of the optical element mounting substrate 2 in the package 4. As indicated by the arrow B in FIG. 7A, the substrate surface 28 of the optical element mounting substrate 2 is caused to face the surface on which the projections 18 are formed in the package 4, with the substrate surface 28 of the optical element mounting substrate 2 being directed downwardly (in FIG. 7A), the optical element mounting substrate 2 is caused to overlap on the base portion 31 of the package 4, and the projections 18 are inserted and fitted into the V-shaped grooves 9.
FIG. 8 is a cross-sectional view showing an fitted condition of the projections 18 into the V-shaped grooves 9. As shown in FIG. 8, the cross section of the projections 18 is formed into an arcuate shape at their ends, and the ends contact the groove surfaces of the V-shaped grooves 9. Then, thus, the projections 18 are inserted and fitted into the V-shaped grooves 9 so that the package 4 and the optical element mounting substrate 2 are positioned with each other and the array type optical element 1 and the input/output optical fibers 7 are centered and optically coupled to each other.
Under the condition in which the optical element mounting substrate 2 and the package 4 are overlapped with each other as described above, the region (indicated by reference character A in FIG. 7A) between an inner wall surface 32a of the side wall 32 of the package 4 and the optical element 1 is sealed with resin. Thus, the input/output optical fibers 7 are bonded and fixed to the package 4, at the same time, the optical element 1 of the optical element mounting substrate 2 as a whole is covered by the resin to be sealed. Furthermore, the optical element mounting substrate 2 is fixed to the package 4.
The package 4 in which the optical element mounting substrate 2 is provided is mounted on a lead frame package 11 with the optical element mounting substrate 2 being directed downwardly as indicated by the arrow C in FIG. 7A, and fixed by adhesives 30.
The optical module 100 shown in FIGS. 7A and 7B is constructed as described above. This optical module 100 is constructed so as to be electrically connectable to a circuit of a mounting substrate (not shown) through a plurality of lead terminals 17 formed in the lead frame package 11.
Incidentally, reference numeral 20 in FIGS. 7A and 7B indicates an opening portion, which is a hole for wire bonding (lines made of gold are arranged from the optical element mounting substrate 2 to the lead frame package 11) and injecting the adhesives 30.
As described above, with the optical module 100, only the projections 18 of the package 4 are inserted and fitted in the V-shaped grooves 9 of the optical element mounting substrate 2 so that the array type optical element I and the input/output optical fibers 7 are centered and optically coupled to each other. Thus, it is possible to provide the optical module that may optically and directly coupling the array type optical element 1 and the input/output optical fibers 7 with each other without any lens without using an expensive device.
However, although the resin made package 4 is molded by transfer molding, injection molding of the resin or the like, there is a problem in that it is technically difficult to form the projections 18 into a desired shape, for example, an arcuate shape having a diameter of about 125 xcexcm.
Namely, in order to form the package 4, as shown in FIG. 9, the resin forming the package 4 is caused to flow into a mold 33 having a groove 33a for forming the projection 18 and cured. At this time, in order to form the projection 18 to have an exact size and an exact shape, it is necessary to transfer the groove 33a of the mold 33 exactly with the precision of xc2x11 xcexcm. In order to attain this, a high processing technique is required. Also, in view of the fact that it is difficult to exactly evaluate the dimension of the machined mold, it is difficult to enhance the dimensional precision of the mold 33 by feeding back the information of the dimensional error of the molded product.
For this reason, it is technically difficult to form the projection 18 with a high precision and exactly in accordance with the design as described above. Due to this, it is difficult to, precisely position the package 4 and the optical element mounting substrate 2 with each other. Accordingly, it is difficult to perform the precise positioning of the relative positional relationship between the optical element 1 and the input/output optical fiber 7 and to stably realize the high optical connection.
The present invention has been made in view of the above, and an object of the present invention is therefore to provide an optical module in which an optical element mounting substrate and a package may be arranged exactly with each other.
In order to attain this and other objects, according to a first aspect of the invention, there is provided an optical module having an optical element mounting substrate on which an optical element is mounted, and a package made of resin, on which the optical element mounting substrate is arranged, characterized in that a substrate side positioning groove portion is formed in a substrate surface of the optical element mounting substrate, a package side positioning groove portion is formed in the package, the package side positioning groove portion facing the substrate side positioning groove portion by arranging the optical element mounting substrate to face the package, and a positioning member is inserted between the package side positioning groove portion and the substrate positioning groove portion which face each other.
According to a second aspect of the present invention, there is provided an optical module provided with the structure according to the first aspect of the invention, and characterized in that at least one of the substrate side positioning groove portion and the package side positioning groove portion is a groove having a substantially V-shaped groove in cross section.
According to a third aspect of the invention, there is provided an optical module provided with the structure according to the first aspect of the invention, and characterized in that at least one of the substrate side positioning groove portion and the package side positioning groove portion is a groove having an arcuate groove in cross section.
According to a fourth aspect of the invention, there is provided an optical module provided with the structure according to the first aspect of the invention according to the first aspect of the invention, and characterized in that at least one of the substrate side positioning groove portion and the package side positioning groove portion has such a shape that the groove portion may engage with the positioning member with almost no gap.
According to a fifth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to fourth aspects of the invention, and characterized in that the positioning member is a columnar member. According to a sixth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to fifth aspects of the invention, and characterized in that a linear expansion coefficient of the positioning member is 1xc3x9710xe2x88x926/K or less.
According to a seventh aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to sixth aspects of the invention, and characterized in that the positioning member is an optical fiber.
According to an eighth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to seventh aspects of the invention, and characterized in that the substrate side positioning groove portions are formed on both sides of the optical element.
According to a ninth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to eighth aspects of the invention, and characterized in that a length of a part of the positioning member clamped between the optical element mounting substrate and the package is one third or more of the substrate side positioning groove portion.
According to a tenth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to ninth aspects of the invention, and characterized in that the package has a base portion in which the package side positioning groove is formed, and a side wall which is formed in an upright condition at an end face of the base portion, and a hole for insertion of the positioning member is formed so as to be continuous with the package side positioning groove portion.
According to an eleventh aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to tenth aspects of the invention, and characterized in that an optical fiber to be optically coupled to the optical element is mounted on the package, and the optical fiber and the positioning member are arranged such that they are substantially in parallel with each other along their longitudinal direction and the centers thereof are substantially in the same flat plane.
According to a twelfth aspect of the invention, there is provided an optical module provided with the structure according to anyone of the first to eleventh aspects of the invention, and characterized in that the optical module further comprises an optical fiber to be optically coupled to the optical element, wherein the optical fiber is optically coupled directly to the optical element.
According to the present invention, a substrate side positioning groove portion is provided in a substrate surface of the optical element mounting substrate, a package side position groove portion is formed in the package, the optical element mounting substrate and the package are arranged with the substrate side positioning groove portion and the package side positioning groove portion facing each other, and a positioning member is inserted between the package side positioning groove portion and substrate positioning groove portion which face each other. The package positioning portion is in the form of a groove as described above. Thus, it is possible to readily form the mold for molding the package with high precision. Accordingly, it is possible to readily form the package provided with the exact positioning groove portion, as a result of which it is possible to provide the optical module that may exactly provide the optical element mounting substrate and the package in place.
In the case where at least one of the substrate side positioning groove portion and the package side positioning groove portion is substantially in the form of a V-shape or in the case where at least one of the substrate side positioning groove portion and the package side positioning groove portion is in the arcuate form, the substantially V-shaped groove or the arcuate groove may readily be formed with high precision. It is therefore possible to enhance the positioning precision of the optical element mounting substrate and the package.
In particular, in the case where at least one of the substrate side positioning groove portion and the package side positioning groove portion has a form to fit the positioning member with almost no gap, the grooves are intimately fitted with the positioning member so that the positional displacement of the positioning member to the positioning groove portions may be avoided. It is thus possible to considerably enhance the positioning precision of the optical element mounting substrate and the package.
In the case where the positioning member is the columnar member, for example, in the case where at least one of the substrate side positioning groove portion and the package side positioning groove portion is substantially in the form of a V-shape, the columnar positioning member may be arranged in the substantially V-shaped groove without any displacement.
In the case where the linear expansion coefficient of the positioning member is at 1xc3x9710xe2x88x926/K or less, the thermal expansion or the thermal shrinkage of the positioning member due to the temperature change is very small whereby it is possible to substantially suppress the positional displacement of the package and the optical element mounting substrate caused by the temperature change.
In the case where the positioning member is the optical fiber, it is possible to form the optical fiber with very high precision, and the optical fiber is in the form of a columnar shape with its linear expansion coefficient of 1xc3x9710xe2x88x926/K or less. Thus, the optical fiber as the positioning member is inserted and fitted between the substrate side positioning groove portion and the package side positioning groove portion, and the package may be positioned to the optical element mounting substrate as designed. In addition, it is possible to suppress the positional displacement of the optical element mounting substrate and the package caused by the temperature change.
In the case where the substrate side positioning portions are formed on both sides of the optical element, it is possible to arrange the optical element to the package in the position as designed. It is thus possible to considerably enhance the optical coupling rate of, for example, the optical element and the optical fiber that is the object to be optically coupled to and mounted on the package.
In the case where the length of the part of the positioning member clamped between the optical element mounting substrate and the package is one third or more of the full length of the substrate side positioning groove portion, there is no fear that the positioning member is too short and tilted to the package. It is thus possible to align the package and the optical element mounting substrate to each other without fail.
In the case where the hole through which the positioning member passes and which is continuous with the package side positioning groove portion, the positioning member is inserted and arranged into the package side positioning groove portion through the hole of the side wall of the package, so that the positioning member may be positioned in a set position with ease.
In the case where an optical fiber to be optically coupled to the optical element is fixed to the package, and the optical fiber and the positioning member are arranged such that they are substantially in parallel with each other along their longitudinal direction and the centers thereof are substantially in the same flat plane, it is possible to position the optical element and the fiber to each other with the optimum positioning precision and to perform the very good optical coupling of the optical element and the fiber.
As described above, according to the present invention, it is possible to position the optical element and the optical fiber to each other with very high precision. It is thus possible to optically couple the optical element and the optical fiber directly to each other without any lens and without using an expensive device to thereby reduce the size of the optical module.